Story: Natural environment

Page 3 – Climate

New Zealand is roughly midway between Antarctica and the tropics, lying between 34° and 47° latitude south. This spans the ‘roaring forties’, which can bring high winds and stormy seas to much of the country. The northern outlying islands are subtropical, while those in the south are subantarctic. Between these extremes, New Zealand’s climate is cool to temperate, but can vary widely, even within one day. The saying ‘raining at seven, fine by eleven’ often rings true for the weather forecasters.

The weather pattern

At New Zealand’s location, warm moist air from the tropics meets cold dry air from Antarctica. The two don’t mix: they twist around and bump into each other. These swirling air masses sweep over New Zealand from the west.

Large volumes of stable, dry, descending air are known as high-pressure systems, often termed ‘highs’, which bring settled weather. Eastward-travelling highs cross the country every six to seven days. Between the highs are areas of unstable, ascending air known as low-pressure systems, or ‘lows’.

Within the air systems there are often cold fronts – the boundary between a cold and warm air mass. These fronts produce one of the most common weather sequences. As the front approaches from the west, north-westerly winds strengthen and cloud increases. It then rains for several hours as the front passes over, with a subsequent change to cold showery south-westerly winds.

The weather consists largely of this endless procession of highs and lows sweeping over the country.

The seasons

New Zealand’s seasons roughly follow this pattern:

Spring arrives in September and October, as the days lengthen and the yellow kōwhai blooms mark the end of colder weather. Springtime is often windy, as variable weather sweeps over the country. Average temperature: 12.1°C.

Summer is cool to mild in the south, and mild to warm in the north. Although Christmas Day is officially in summer, the weather is often still unpredictable. As the days shorten in January and February, there are long fine spells. Average temperature: 16.6°C.

Autumn is the most settled time. In the far north an extended ‘Indian summer’ is a very real prospect. Average temperature: 13.3°C.

Winter is cold, especially in the South Island and inland areas. Southerly blasts coat the mountains on both islands with snow. Average temperature: 8.3°C.

However, it is quite possible to experience four seasons in one day.

Wind

The wind comes to New Zealand mainly from the west. In New Zealand's southern latitudes there is no other land apart from the tip of South America. Nothing gets in the way of these ‘brave west winds’, as mariners call them; they finally hit New Zealand after travelling 10,000 km.

An ill wind

A paradoxical wind, the nor’wester dumps metres of rain on the West Coast, then rises over the Southern Alps and descends on the Canterbury Plains in hot, dry gusts. When Canterbury’s dust-laden nor’wester blows, suicide rates go up and people get headaches or become grouchy. At gale force, it does serious damage to farms and buildings. Known to Māori as parera, it is one of several ‘bitter’ seasonal winds, including France’s mistral, California’s Santa Ana, and the Chinook of western Canada. And yet in winter Canterbury’s ‘mad dog’ is tamed, bringing welcome mild weather.

The early European explorers who ventured onto upland areas were blown off their feet. Māori would have shown little surprise – they had more than a dozen terms for the different winds.

One of the most readily recognisable regional winds is Canterbury’s nor’wester – a hot, dry wind. And the whole country knows the southerly, which blasts up from Antarctica.

Rainfall

The distribution of New Zealand’s ample rainfall is greatly affected by the mountains. The general rule is that east is drier, west is wetter. The mean annual rainfall varies from 300 mm in Central Otago to over 6,000 mm at Milford Sound, on the south-west coast. The highest recorded annual rainfall was over 18,000 mm, measured at Cropp River (Hokitika catchment) on the West Coast. However, most areas receive 600–1,500 mm, and large areas of both islands receive over 2,500 mm a year.

Sunshine

As New Zealand lies just west of the International Date Line, Chatham Islanders are the first people to see the sun rise each day. The sun beams down on Blenheim and Nelson (in the South Island), and Whakatāne (in the North Island), where average annual sunshine hours exceed 2,350. The Bay of Plenty and Napier also bask in the sun. Many retired people move to the sunnier northern and eastern areas. But the New Zealand sun is especially harsh, and Auckland has the highest rate of melanoma (skin cancer) in the world.

Much of the country gets at least 2,000 sunshine hours a year, and even rainy Westland, which tourists dub ‘Wetland’, has 1,800 hours. Annual sunshine hours drop to around 1,700 a year in Southland and coastal Otago.

A nice cold beer

In Central Otago they are used to the chill, but in July 1991 many hardy locals were tested. When a high-pressure system brought clear skies and intense frosts, the temperature dropped to -15°C for days on end. For the first time in at least 100 years the Shotover River froze over. Power lines snapped, weighed down by sausages of ice. Sheep’s coats froze to the ground, water pipes burst and diesel fuel in engines turned to sludge. But perhaps the direst challenge was when the beer inside pubs froze.

Temperature

Northland’s reputation as the ‘winterless north’ is well earned. By contrast, in parts of the deep south the winter chill approaches that of regions at similar latitudes such as Europe. Average coastal temperatures range from about 15°C in Northland to about 10°C in Southland. January and February are the warmest months, and July is the coldest.

The highest recorded temperature of 42.4°C occurred in the South Island simultaneously at Rangiora (Canterbury) and Jordan (Marlborough) on 7 February 1973. And on 3 July 1995 the mercury dropped to a record -21.6°C at Ophir, Central Otago.